Example 1.3

Example . (vii) Molality : Molality ( m ) is defined as the number of moles of the solute per kilogram (kg) of the solvent and is expressed as: Molality (m) = Moles of solute Mass of solvent in kg ( . ) For example, . mol kg – (or . m) solution of KCl means that mol ( . g) of KCl is dissolved in kg of water. Each method of expressing concentration of the solutions has its own merits and demerits. Mass %, ppm, mole fraction and molality are independent of temperature, whereas molarity is a function of temperature. This is because volume depends on temperature and the mass does not. Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature. It depends upon the nature of solute and solvent as well as temperature and pressure. Let us consider the effect of these factors in solution of a solid or a gas in a liquid.